C.2.7 make macro=value and Submakes

A command-line variable definition such as foo=bar overrides any
definition of foo in a makefile. Some make
implementations (such as GNU make) propagate this
override to subsidiary invocations of make. Some other
implementations do not pass the substitution along to submakes.

You have a few possibilities if you do want the foo=bar override
to propagate to submakes. One is to use the -e
option, which causes all environment variables to have precedence over
the makefile macro definitions, and declare foo as an environment
variable:

$ env foo=bar make -e

The -e option is propagated to submakes automatically,
and since the environment is inherited between make
invocations, the foo macro is overridden in
submakes as expected.

This syntax (foo=bar make -e) is portable only when used
outside of a makefile, for instance from a script or from the
command line. When run inside a make rule, GNU
make 3.80 and prior versions forget to propagate the
-e option to submakes.

Moreover, using -e could have unexpected side effects if your
environment contains some other macros usually defined by the
makefile. (See also the note about make -e and SHELL
below.)

If you can foresee all macros that a user might want to override, then
you can propagate them to submakes manually, from your makefile:

foo = foo
one:
@echo $(foo)
$(MAKE) foo=$(foo) two
two:
@echo $(foo)

Another way to propagate a variable to submakes in a portable way is to
expand an extra variable in every invocation of ‘$(MAKE)’ within
your makefile:

Users must be aware that this technique is in use to take advantage of
it, e.g. with make foo=bar SUBMAKEFLAGS='foo=bar', but it
allows any macro to be overridden. Makefiles generated by
automake use this technique, expanding $(AM_MAKEFLAGS)
on the command lines of submakes (see Automake in GNU Automake).